1. Field of the Invention
The present invention generally relates to the field of air cleaning systems. More specifically, the present invention relates to an ion filtration device (“IFD”) for cleaning air by use of electrostatic ion attraction.
2. Description of the Related Art
Air having a high concentration of suspended particles (hereinafter, “dirty air”) can pose a health hazard to living beings from breathing the dirty air. The dirty air can also cause a higher rate of deposition of settled suspended particles (e.g., dust) thus causing more frequent cleaning of surfaces that are desired to be kept clean (e.g., surfaces inside a home).
In farming, high aerosol concentrations are found in situations such as poultry sheds and intensive pig rearing sheds etc., and thus the health of both workers and animals is at risk.
In industry a variety of processes such as welding, grinding, smelting and use of internal combustion engines in confined spaces all produce high concentrations of suspended particles in enclosed spaces.
In social and domestic situations, suspended particles are produced by tobacco smoking. Sneezing can produce aerosols of bacteria and viruses. Allergy producing pollen is found in high concentrations at various times of the year. Dust mite allergen particles are produced when making up beds and enter the air as suspended particles.
Conventional air cleaners may remove particles from the air by trapping them either in filters as in a filtration air cleaner (FAC), or by collecting them on plates as in an electrostatic precipitation air cleaner (ESPAC). The filters or plates may then be disposed of, washed or replaced.
Disadvantages of FAC devices include a drop in efficiency of the filter over time as particles clog the filter; the need for a fan powerful enough to overcome the partially-clogged filter; noise and power consumption associated with the fan; and the need to replace the filters regularly.
Disadvantages of ESPAC devices include: a need for costly shielding of high voltage plates; loss of efficiency and generation of ozone caused by electrical breakdown and leakage between the high voltage plates; and a need to space the high voltage plates relatively far apart to reduce electrical breakdown in the air between the high voltage plates, thus increasing size and reducing efficiency.
Electrostatic precipitation air cleaners operate by attracting charged particles and ions to collection plates charged with an opposite electrical charge from that of the charged particles and ions. A variation of the ESPAC device is to replace the high voltage plates with an air passage, the air passage having at least a portion thereof having an electrical potential, electrets properties, electrostatic properties, or the like. An example of such a device known in the art is U.S. Pat. No. 6,749,669 to Griffiths, et al., the contents of which are incorporated by reference herein.
However, the particles and ions that are to be collected may not ordinarily be in a charged state, so charge must be introduced onto the particles and ions in order to attract them to the collection plates. Conventional electrostatic air cleaners of this kind introduce charge onto the particles and ions as they leave the cleaner by use of an ionizer to electrically ionize the gas or air stream. The ionizer may include a primary corona discharge emitter and a secondary corona discharge emitter at a lower potential relative to the primary emitter. The primary corona discharge emitter is connected to a high negative potential while the secondary corona discharge emitter is connected to electrical ground. The primary corona discharge emitter may be a needle having a sharp tip and the secondary corona discharge emitter may be a needle having a relatively blunt tip.
Since the ionizer imparts charge upon particles and ions as they leave the cleaner, the ions so charged must travel back to an air inlet of the conventional electrostatic air cleaner in order to be collected. This presents a disadvantage of the known art, because some particles so ionized may not return to the air inlet, and particles which do return to the air inlet may lose some or all of their charge before returning. Unless the electrostatic air cleaner is operating in a confined space, few adequately charged ions may return to the air inlet. Consequently, there is a need for a more efficient electrostatic air cleaner